Stroke is the leading cause of chronic disability and the third most common cause of death in the United States. Nearly 90% of stroke patients are ischemic and result from occlusion of a cerebral artery. A common complication of stroke is body/brain temperature increase which occurs in 50% patients within 48 hours following an ischemic insult. Evidence from both clinical and preclinical studies supports that brain temperature increase negatively correlates with the outcome of stroke and it has adverse effects on treatment regimens that work under normothermic conditions. Although it is well known that increase in brain temperature is deleterious for the injured brain, the mechanisms underlying its deleterious actions are unknown. As the temperature increase affects final outcome of stroke, it requires further study. We have preliminary data on the actions of hyperthermia in focal models of brain ischemia. We found that hyperthermia, induced immediately prior to ischemia, increases infarct volume, worsens perfusion deficits (area without blood supply), leads to increased disruption of the blood-brain barrier and abolishes the efficacy of thrombolysis. Hyperthermia also exacerbates the losses of collagen type IV, a major structural protein of the microvascular basal lamina, likely through the increasing activities of matrix metalloproteinase-9, a proteolytic enzyme. The proposed studies in this R15 application will test the hypothesis that increased brain temperature exacerbates microvascular dismantlement of the basal lamina through increased actions of MMPs following an acute ischemic event. There are two specific aims. Aim I: Determine the effects of post ischemic hyperthermia on the damage of the microvasculature in the inured brain. Specifically, we will systematically characterize the effects of hyperthermia induced post ischemia on the losses of collagen type IV. Furthermore, we will study the effects of hyperthermia on MMP activities. We expect that hyperthermic treatment will worsen the losses of collagen type IV in the ischemic injured brain, and this treatment will also elevate activations of MMP9. Aim 2: Investigate if MMP9 has a significant role in hyperthermia-enhanced microvascular damage and subsequent injury outcomes. We expect that MMP9 plays a significant role and, therefore, knockout of this enzyme will reduce hyperthermia- enhanced microvascular damage and subsequent injury outcomes. The extensive works proposed here investigate the molecular mechanisms underlying microvascular injury in acute stroke and should provide significant insight about temperature increase- enhanced damage of microvascular structures following ischemic brain injury. The damage of the microvasculature has been linked to neuronal death following ischemia and thus the protection of the microvasculature may be an important target for the development of novel therapeutic approaches for ischemic brain injury. Therefore, the information obtained from the proposed studies should benefit the clinical management of stroke patients, especially in the setting of increased body temperature. PUBLIC HEALTH RELEVANCE: Body temperature increase can adversely affect stroke outcome, especially when it occurs during an early phase of stroke. The studies proposed here examine how the temperature increase affects microcirculation and neuronal death in animal model of stroke. Therefore, the information obtained from the proposed studies should benefit the development of new therapeutic strategies and improve the clinical management of stroke patients.